The present invention relates to a supporting apparatus for an objective lens used in an optical device such as an optical scanner or the like or used in a data recording/reproducing apparatus which records/writes data with respect to an optical recording medium such as an optical disk drive, postscript type disk drive, phase change disk drive, CD-ROM, DVD, optical card, or the like, and also relates to a supporting spring apparatus for an optical movable part for rotatably supporting a galvano mirror for use in an optical device such as, for example, an optical scanner.
Conventionally, an optical element internally having a movable part or a movably supported optical element is used in various optical devices as described above. For example, in an optical element such as a galvano mirror, an optical constituent element such as an internal mirror or the like is rotatably supported.
In many cases, a supporting apparatus based on a spring has been conventionally used as an apparatus for rotatably supporting an optical constituent element or optical element of a small size. The supporting apparatus of this type supports a movable part by a spring, and the movable part is rotatably supported about a predetermined axis.
Since the supporting apparatus using the spring as stated above allows the movable member to be rotated by the deformation of the spring, the apparatus has a predetermined restoring force, i.e., a predetermined spring constant if the movable member rotates. The supporting apparatus of this type preferably possesses characteristics of having a small spring constant in a case where the movable member rotates about the rotation axis and having a small spring constant in a case where the movable member moves in a direction perpendicular to the rotation axis. With such characteristics, this movable member is rotatable about the predetermined rotation axis with a small resistance and moves less in a direction perpendicular to the rotation axis, with the result that the movable member is accurately, rotatably supported about the predetermined rotation axis.
Due to this, according to the conventional supporting spring apparatus stated above, a curved spring is used as shown in FIG. 13. Specifically, in FIG. 13, reference numeral 101 denotes a fixed member on a fixed side and 102 denotes a movable member. The movable member 102 is rotatably supported about a predetermined rotation axis R with respect to the fixed member 101 by a pair of springs 103. Each of the springs 103 is formed out of a thin plate of spring material such as beryllium-copper alloy and is curved. The central portion 104 of the curved spring 103 is positioned in the neighborhood of the rotation axis R. whereas the curved portions 105 on both ends thereof are positioned distant from the rotation axis R.
If the movable member 102 is rotated, the central portion in the neighborhood of the rotation axis R and the both fixed end portions of the spring 103 have the highest bending stress. As a result, bending deformation centered about the central portion 104 occurs to thereby rotatably support the movable member 102 about the rotation axis R. In addition, if the movable member is moved in a direction perpendicular to the rotation axis R, parallel to, for example, the longitudinal direction of FIG. 13 or perpendicular to the longitudinal direction of FIG. 13, then bending or shear deformation occur to the respective portions of the curved spring 103 in a direction parallel to the plane direction thereof, respectively.
Since the spring 103 is of thin plate shape, the ratio of a plate thickness to a width is high. Owing to this, rigidity, i.e., a spring constant against simple bending deformation in a direction perpendicular to the plane direction or in a plate thickness direction become the smallest, whereas rigidity, i.e., a spring constant against twisting deformation or bending or shearing deformation along plane direction is larger. If the movable member 102 is rotated, that is, if simple bending deformation in the plate thickness direction occurs to the central portion 104, the movable member 102 has a small spring constant. If the movable member 102 is moved in a direction perpendicular to the rotation axis R, that is, if bending or shearing deformation along plane direction occurs to the respective portions of the movable member 102, then the member 102 has a large spring constant. This makes it possible that the movable member 102 is rotatably supported about the rotation axis R with a low resistance and that the moving amount of the movable member 102 in the direction perpendicular to the rotation axis is smaller, thereby accurately supporting the movable member 102.
In the supporting spring apparatus of this type, it is preferable that the displacement in the direction perpendicular to the rotation axis R is as little as possible. To do so, the width of the curved spring 103 is preferably large. If the curved spring 103 is wider, the spring constant at which the central portion 104 is subjected to bending deformation becomes larger accordingly. The resistance with which the movable member 102 is rotated becomes disadvantageously higher.